The present invention relates to a method and a device for controlling and possibly also accelerating the flow through a preferably continuously operating distillation apparatus for separating components of a mixture, particularly a dissolved substance, such as an oil, a wax, a polishing agent or alike from a liquid mixture, containing particularly containing a chlorinated solvent, such as tri- or perchlorethylene, wherein, by using the heat pump principle, the heat emitted upon condensation of the distillate is transferred to the vaporizer of a refrigeration circuit, in which the refrigeration fluid by means of additional compressor work returns this heat via a condensor of the refrigeration circuit to the boiling liquid.
In times of rapidly rising prices of solvents and concern about the environment, there are good reasons to increasingly distillate and re-circulate various solvents. The reuse of solvents by a distilling process is nothing new in itself. Traditionally, this is done to recover chlorinated solvents in various washing processes, in which e.g. tri- or perchlorethylene is used as a solvent.
Heretofore, distilling has generally been performed by electrical heating or hot water or steam as a heating medium, and air or water as a cooling medium. However, in the literature of refrigeration technology, examples have been generally given as to distillation by using the heat pump principle. Consequently such a method per se is not a novel concept.
The object of the invention, however, is to achieve a more energy-saving, automatically operating system, particularly for a continuous operation. In the first place, the system should enable the distillation of solvents of the kind including tri- and perchlorethylene or freones, but it should also be possible to use the system for other distillable liquids.
The boiling point of a liquid to be distilled is generally dependent on how many and to what degree other substances are carried as a solute. In case of washing products in the mechanical engineering industry, the solute is mostly an oil, a wax or some polishing agent. These solutes influence the boiling temperature in such a way that e.g. an increased percentage of mineral oil dissolved in the washing liquid raises the boiling temperature most considerably. For instance, in case of mineral oil dissolved in trichlorethylene, the boiling temperature will progressively increase from about 87.degree. C. at zero mineral oil contents to about 110.degree. C. at a mineral oil percentage of 60% by volume. In order to simplify matters, the discussion below will concern trichlorethylene as a solvent and mineral oil dissolved therein.
In a distillation process, it is important that the necessary heat is not supplied at a temperature being so high that the solvent will be thermally disintegrated. In case of trichlorethylene, it is necessary not to expose the solution to a temperature above 100.degree. C. This means, that when distilling trichlorethylene, the mineral oil percentage must not exceed about 45% by volume. In practice, the mineral oil percentage should not exceed 30% by volume.
Even the weight or density of the liquid is dependent on the mineral oil percentage. Thus, the specific weight or density decreases linearly from a value of 1.5 for pure trichlorethylene to 0.9 for pure mineral oil, and the difference in density of different oil mixtures is such that it can be used for separating solvents having respectively a high and a low oil percentage in the distiller.